This proposal involves a request for NIH support for a Workshop on Photosensitizing Agents in the Therapy of Neoplastic Disease. Recent reports have indicated that a derivative of hematoporphyrin is a useful tumor-localizing agent. Furthermore, irradiation of porphyirn-loaded tissues results in marked selective toxicity to tumor loci. This workshop is designed to bring together workers in the following fields: Porphyrin chemistry and photo-chemistry, Fluorescence spectroscopy, Biochemical pharmacology, Photo-physics, Clinical medicine. An exchange of information among these individuals shold result in an improved outlook for porphyrin research and further drug development.